1. Field of the Invention
The present invention relates to a plant for making biodiesel fuel, and a method of making the fuel.
2. Description of the Related Art
In a process of making biodiesel fuel from soy bean oil, tallow (yellow grease) or other raw material containing fatty acid esters, generally the raw material is processed with methanol and potassium hydroxide or sodium hydroxide.
In U.S. patent application Ser. No. 10/235,065, filed Sep. 4, 2002, in the name of the present inventor (referred to herein as “Continuous Flow Application”), and incorporated by reference herein, there is disclosed a continuous flow process for forming biodiesel from food oils such as yellow grease, vegetable oil, soy bean oil, or other raw material having fatty acid esters. The Continuous Flow Application also contains a description of the conventional batch process.
In either the continuous or batch process for making biodiesel, the raw material, the yellow grease, vegetable oil, soy bean oil, or other raw material having fatty acid esters, often comes from or includes waste oil from cooking. This waste oil is processed with methanol and preferably with a catalyst such as sulfuric acid (H2S) in a first reaction vessel, such as shown in the Continuous Flow Application.
The methanol reacts with the fatty acid in the oil and produces a methyl ester material. Then, the methyl ester material (treated raw material) is sent to a first settling tank where the sulfuric acid (H2S) and a small amount of methanol separate and may be drained and reused. The treated separated raw material is then reheated in a batch process, or kept heated in a continuous process, and mixed in a second reaction vessel with more methanol, and also with a catalyst, such as potassium hydroxide (KOH) or sodium hydroxide (NaOH). A reaction known as esterification takes place, creating a mixture of raw or crude biodiesel fuel, and excess methanol, and perhaps some catalyst. This mixture is sent to a second settling tank. In this second settling tank, the crude biodiesel fuel rises to the top, while the methanol, glycerol and some fatty acid soap sink to the bottom.
To minimize the amount of soap, an excess amount of methanol is typically used. That is, more methanol is used than is necessary to react with the amount of raw material. It is desirable to recover the excess methanol. Moreover, it is desirable to remove any entrained methanol and any other unreacted substances from the crude biodiesel.
In the above conventional batch process and the continuous flow application process and plant, there is no pressure applied to the fluids as they flow through the plant. Also, the fluids are reacted in vessels. There are four vessels in the process, because there are two reactions and two subsequent settling processes required. The temperature of the fluid must be kept below the boiling point of methanol to avoid the escape of methanol vapors which are hazardous. Moreover, there is no pressure applied to the fluid other than in the continuous flow application the fluid is continuously pumped through the plant. The present inventor has recognized that because of the conventional limitations of operating sufficiently below the boiling point of about 149° F. of methanol, and operating without added pressure (because of the reaction vessels), the reaction can only take place so fast.